PROTOCOL FOR THE USE OF EXTRACTIVE FOURIER TRANSFORM INFRARED

							      PROTOCOL FOR THE USE OF EXTRACTIVE FOURIER TRANSFORM

  INFRARED (FTIR) SPECTROMETRY FOR THE ANALYSES OF GASEOUS

                EMISSIONS FROM STATIONARY SOURCES

1.0   INTRODUCTION
      The purpose of this addendum is to set general

guidelines for the use of modern FTIR spectroscopic methods

for the analysis of gas samples extracted from the effluent

of stationary emission sources.     This addendum outlines

techniques for developing and evaluating such methods and
sets basic requirements for reporting and quality assurance

procedures.

1.1   NOMENCLATURE

      1.1.1   Appendix A to this addendum lists definitions of

the symbols and terms used in this Protocol, many of which

have been taken directly from American Society for Testing

and Materials (ASTM) publication E 131-90a, entitled
"Terminology Relating to Molecular Spectroscopy."

      1.1.2   Except in the case of background spectra or

where otherwise noted, the term "spectrum" refers to a

double-beam spectrum in units of absorbance vs. wavenumber
   -1
(cm ).
      1.1.3   The term "Study" in this addendum refers to a

publication that has been subjected to EPA- or peer-review.

2.0    APPLICABILITY AND ANALYTICAL PRINCIPLE

      2.1   Applicability.   This Protocol applies to the

determination of compound-specific concentrations in single-

and multiple-component gas phase samples using double-beam
absorption spectroscopy in the mid-infrared band.   It does

not specifically address other FTIR applications, such as

single-beam spectroscopy, analysis of open-path (non-

enclosed) samples, and continuous measurement techniques.

If multiple spectrometers, absorption cells, or instrumental

linewidths are used in such analyses, each distinct

operational configuration of the system must be evaluated

separately according to this Protocol.

    2.2   Analytical Principle.

    2.2.1   In the mid-infrared band, most molecules exhibit

characteristic gas phase absorption spectra that may be

recorded by FTIR systems.   Such systems consist of a source

of mid-infrared radiation, an interferometer, an enclosed

sample cell of known absorption pathlength, an infrared

detector, optical elements for the transfer of infrared

radiation between components, and gas flow control and

measurement components.   Adjunct and integral computer

systems are used for controlling the instrument, processing

the signal, and for performing both Fourier transforms and

quantitative analyses of spectral data.

    2.2.2   The absorption spectra of pure gases and of

mixtures of gases are described by a linear absorbance

theory referred to as Beer's Law.   Using this law, modern

FTIR systems use computerized analytical programs to

quantify compounds by comparing the absorption spectra of

known (reference) gas samples to the absorption spectrum of

the sample gas.   Some standard mathematical techniques used
for comparisons are classical least squares, inverse least

squares, cross-correlation, factor analysis, and partial

least squares.    Reference A describes several of these

techniques, as well as additional techniques, such as

differentiation methods, linear baseline corrections, and

non-linear absorbance corrections.

3.0   GENERAL PRINCIPLES OF PROTOCOL REQUIREMENTS

      The characteristics that distinguish FTIR systems from

gas analyzers used in instrumental gas analysis methods

(e.g., Methods 6C and 7E of appendix A to part 60 of this

chapter) are: (1) Computers are necessary to obtain and

analyze data; (2) chemical concentrations can be quantified

using previously recorded infrared reference spectra; and

(3) analytical assumptions and results, including possible

effects of interfering compounds, can be evaluated after the

quantitative analysis.    The following general principles and

requirements of this Protocol are based on these

characteristics.

      3.1   Verifiability and Reproducibility of Results.

Store all data and document data analysis techniques

sufficient to allow an independent agent to reproduce the

analytical results from the raw interferometric data.

      3.2   Transfer of Reference Spectra.   To determine

whether reference spectra recorded under one set of

conditions (e.g., optical bench, instrumental linewidth,

absorption pathlength, detector performance, pressure, and

temperature) can be used to analyze sample spectra taken
under a different set of conditions, quantitatively compare

"calibration transfer standards" (CTS) and reference spectra

as described in this Protocol.    (Note: The CTS may, but need

not, include analytes of interest).     To effect this, record

the absorption spectra of the CTS (a) immediately before and

immediately after recording reference spectra and (b)

immediately after recording sample spectra.

    3.3   Evaluation of FTIR Analyses.    The applicability,

accuracy, and precision of FTIR measurements are influenced

by a number of interrelated factors, which may be divided

into two classes:

    3.3.1   Sample-Independent Factors.    Examples are system

configuration and performance (e.g., detector sensitivity

and infrared source output), quality and applicability of

reference absorption spectra, and type of mathematical

analyses of the spectra.    These factors define the

fundamental limitations of FTIR measurements for a given

system configuration.    These limitations may be estimated

from evaluations of the system before samples are available.

For example, the detection limit for the absorbing compound

under a given set of conditions may be estimated from the

system noise level and the strength of a particular

absorption band.    Similarly, the accuracy of measurements

may be estimated from the analysis of the reference spectra.

    3.3.2   Sample-Dependent Factors.    Examples are spectral

interferants (e.g., water vapor and CO2) or the overlap of
spectral features of different compounds and contamination
deposits on reflective surfaces or transmitting windows.         To

maximize the effectiveness of the mathematical techniques

used in spectral analysis, identification of interferants (a

standard initial step) and analysis of samples (includes

effect of other analytical errors) are necessary.       Thus, the

Protocol requires post-analysis calculation of measurement

concentration uncertainties for the detection of these

potential sources of measurement error.

4.0     PRE-TEST PREPARATIONS AND EVALUATIONS

      Before testing, demonstrate the suitability of FTIR

spectrometry for the desired application according to the

procedures of this section.

      4.1 Identify Test Requirements.   Identify and record

the test requirements described in sections 4.1.1 through

4.1.4 of this addendum.     These values set the desired or

required goals of the proposed analysis; the description of

methods for determining whether these goals are actually met

during the analysis comprises the majority of this Protocol.

      4.1.1   Analytes (specific chemical species) of

interest.     Label the analytes from i = 1 to I.

      4.1.2   Analytical uncertainty limit (AUi).   The AUi is

the maximum permissible fractional uncertainty of analysis

for the ith analyte concentration, expressed as a fraction of

the analyte concentration in the sample.

      4.1.3   Required detection limit for each analyte (DLi,

ppm).    The detection limit is the lowest concentration of an

analyte for which its overall fractional uncertainty (OFUi)
is required to be less than its analytical uncertainty limit

(AUi).

    4.1.4     Maximum expected concentration of each analyte

(CMAXi, ppm).

    4.2   Identify Potential Interferants.    Considering the

chemistry of the process or results of previous studies,

identify potential interferants, i.e., the major effluent

constituents and any relatively minor effluent constituents

that possess either strong absorption characteristics or

strong structural similarities to any analyte of interest.

Label them 1 through Nj, where the subscript "j" pertains to
potential interferants.     Estimate the concentrations of

these compounds in the effluent (CPOTj, ppm).

    4.3   Select and Evaluate the Sampling System.

Considering the source, e.g., temperature and pressure

profiles, moisture content, analyte characteristics, and

particulate concentration), select the equipment for

extracting gas samples.     Recommended are a particulate

filter, heating system to maintain sample temperature above

the dew point for all sample constituents at all points

within the sampling system (including the filter), and

sample conditioning system (e.g., coolers, water-permeable

membranes that remove water or other compounds from the

sample, and dilution devices) to remove spectral

interferants or to protect the sampling and analytical

components.     Determine the minimum absolute sample system

pressure (Pmin, mmHg) and the infrared absorption cell volume
(VSS, liter).   Select the techniques and/or equipment for the

measurement of sample pressures and temperatures.

    4.4   Select Spectroscopic System.    Select a

spectroscopic configuration for the application.

Approximate the absorption pathlength (LS', meter), sample

pressure (PS', kPa), absolute sample temperature TS', and

signal integration period (tSS, seconds) for the analysis.

Specify the nominal minimum instrumental linewidth (MIL) of

the system.     Verify that the fractional error at the

approximate values PS' and TS' is less than one half the
smallest value AUi (see section 4.1.2 of this addendum).

    4.5   Select Calibration Transfer Standards (CTS's).

Select CTS's that meet the criteria listed in sections

4.5.1, 4.5.2, and 4.5.3 of this addendum.

    Note:     It may be necessary to choose preliminary

    analytical regions (see section 4.7 of this addendum),

    identify the minimum analyte linewidths, or estimate

    the system noise level (see section 4.12 of this

    addendum) before selecting the CTS.     More than one

    compound may be needed to meet the criteria; if so,

    obtain separate cylinders for each compound.

    4.5.1     The central wavenumber position of each

analytical region shall lie within 25 percent of the

wavenumber position of at least one CTS absorption band.

    4.5.2     The absorption bands in section 4.5.1 of this

addendum shall exhibit peak absorbances greater than ten

times the value RMSEST (see section 4.12 of this addendum)
but less than 1.5 absorbance units.

    4.5.3    At least one absorption CTS band within the

operating range of the FTIR instrument shall have an

instrument-independent linewidth no greater than the

narrowest analyte absorption band.       Perform and document

measurements or cite Studies to determine analyte and CTS

compound linewidths.

    4.5.4    For each analytical region, specify the upper

and lower wavenumber positions (FFUm and FFLm, respectively)

that bracket the CTS absorption band or bands for the

associated analytical region.    Specify the wavenumber range,

FNU to FNL, containing the absorption band that meets the

criterion of section 4.5.3 of this addendum.

    4.5.5     Associate, whenever possible, a single set of

CTS gas cylinders with a set of reference spectra.

Replacement CTS gas cylinders shall contain the same

compounds at concentrations within 5 percent of that of the

original CTS cylinders; the entire absorption spectra (not

individual spectral segments) of the replacement gas shall

be scaled by a factor between 0.95 and 1.05 to match the

original CTS spectra.

    4.6     Prepare Reference Spectra.

    Note: Reference spectra are available in a permanent
    soft copy from the EPA spectral library on the EMTIC

    (Emission Measurement Technical Information Center)

    computer bulletin board; they may be used if

    applicable.
    4.6.1     Select the reference absorption pathlength (LR)

of the cell.

    4.6.2    Obtain or prepare a set of chemical standards

for each analyte, potential and known spectral interferants,

and CTS.    Select the concentrations of the chemical

standards to correspond to the top of the desired range.

    4.6.2.1     Commercially-Prepared Chemical Standards.

Chemical standards for many compounds may be obtained from

independent sources, such as a specialty gas manufacturer,

chemical company, or commercial laboratory.     These standards

(accurate to within ±2 percent) shall be prepared according

to EPA Traceability Protocol (see Reference D) or shall be

traceable to NIST standards.     Obtain from the supplier an

estimate of the stability of the analyte concentration.

Obtain and follow all of the supplier's recommendations for

recertifying the analyte concentration.

    4.6.2.2     Self-Prepared Chemical Standards.    Chemical

standards may be prepared by diluting certified commercially

prepared chemical gases or pure analytes with ultra-pure

carrier (UPC) grade nitrogen according to the barometric and

volumetric techniques generally described in Reference A,

section A4.6.

    4.6.3    Record a set of the absorption spectra of the

CTS {R1}, then a set of the reference spectra at two or more

concentrations in duplicate over the desired range (the top

of the range must be less than 10 times that of the bottom),

followed by a second set of CTS spectra {R2}.       (If self-
prepared standards are used, see section 4.6.5 of this

addendum before disposing of any of the standards.)     The

maximum accepted standard concentration-pathlength product

(ASCPP) for each compound shall be higher than the maximum

estimated concentration-pathlength products for both

analytes and known interferants in the effluent gas.       For

each analyte, the minimum ASCPP shall be no greater than ten

times the concentration-pathlength product of that analyte

at its required detection limit.

    4.6.4    Permanently store the background and

interferograms in digitized form.     Document details of the

mathematical process for generating the spectra from these

interferograms.    Record the sample pressure (PR), sample
temperature (TR), reference absorption pathlength (LR), and

interferogram signal integration period (tSR).    Signal

integration periods for the background interferograms shall

be ≥tSR.   Values of PR, LR, and tSR shall not deviate by more

than ±1 percent from the time of recording {R1} to that of
recording {R2}.

    4.6.5    If self-prepared chemical standards are employed

and spectra of only two concentrations are recorded for one

or more compounds, verify the accuracy of the dilution

technique by analyzing the prepared standards for those

compounds with a secondary (non-FTIR) technique in

accordance with sections 4.6.5.1 through 4.6.5.4 of this

addendum.

    4.6.5.1    Record the response of the secondary technique
to each of the four standards prepared.

     4.6.5.2   Perform a linear regression of the response

values (dependant variable) versus the accepted standard

concentration (ASC) values (independent variable), with the

regression constrained to pass through the zero-response,

zero ASC point.

     4.6.5.3   Calculate the average fractional difference

between the actual response values and the regression-

predicted values (those calculated from the regression line

using the four ASC values as the independent variable).

     4.6.5.4   If the average fractional difference value

calculated in section 4.6.5.3 of this addendum is larger for

any compound than the corresponding AUi, the dilution
technique is not sufficiently accurate and the reference

spectra prepared are not valid for the analysis.

     4.7   Select Analytical Regions.   Using the general

considerations in section 7 of Reference A and the spectral

characteristics of the analytes and interferants, select the

analytical regions for the application.    Label them m = 1 to

M.   Specify the lower, center and upper wavenumber positions

of each analytical region (FLm, FCm, and FUm, respectively).
Specify the analytes and interferants which exhibit

absorption in each region.

     4.8   Determine Fractional Reproducibility

Uncertainties.    Using appendix E of this addendum, calculate

the fractional reproducibility uncertainty for each analyte

(FRUi) from a comparison of {R1} and {R2}.    If FRUi > AUi for
any analyte, the reference spectra generated in accordance

with section 4.6 of this addendum are not valid for the

application.

    4.9    Identify Known Interferants.   Using appendix B of

this addendum, determine which potential interferants affect

the analyte concentration determinations.    Relabel these

potential interferant as "known" interferants, and designate

these compounds from k = 1 to K.    Appendix B to this

addendum also provides criteria for determining whether the

selected analytical regions are suitable.

    4.10     Prepare Computerized Analytical Programs.

    4.10.1     Choose or devise mathematical techniques (e.g,

classical least squares, inverse least squares, cross-

correlation, and factor analysis) based on equation 4 of

Reference A that are appropriate for analyzing spectral data

by comparison with reference spectra.

    4.10.2     Following the general recommendations of

Reference A, prepare a computer program or set of programs

that analyzes all of the analytes and known interferants,

based on the selected analytical regions (section 4.7 of

this addendum) and the prepared reference spectra (section

4.6 of this addendum).    Specify the baseline correction

technique (e.g., determining the slope and intercept of a

linear baseline contribution in each analytical region) for

each analytical region, including all relevant wavenumber

positions.

    4.10.3     Use programs that provide as output [at the
reference absorption pathlength (LR), reference gas

temperature (TR), and reference gas pressure (PR)] the

analyte concentrations, the known interferant

concentrations, and the baseline slope and intercept values.

If the sample absorption pathlength (LS), sample gas

temperature (TS), or sample gas pressure (PS) during the

actual sample analyses differ from LR, TR, and PR, use a

program or set of programs that applies multiplicative

corrections to the derived concentrations to account for

these variations, and that provides as output both the

corrected and uncorrected values.   Include in the report of

the analysis (see section 7.0 of this addendum) the details

of any transformations applied to the original reference

spectra (e.g., differentiation), in such a fashion that all

analytical results may be verified by an independent agent

from the reference spectra and data spectra alone.

    4.11   Determine the Fractional Calibration Uncertainty.

Calculate the fractional calibration uncertainty for each

analyte (FCUi) according to appendix F of this addendum, and
compare these values to the fractional uncertainty limits

(AUi; see section 4.1.2 of this addendum).   If   FCUi > AUi,

either the reference spectra or analytical programs for that

analyte are unsuitable.

    4.12   Verify System Configuration Suitability.      Using

appendix C of this addendum, measure or obtain estimates of

the noise level (RMSEST, absorbance) of the FTIR system.

Alternatively, construct the complete spectrometer system
and determine the values RMSSm using appendix G of this

addendum.      Estimate the minimum measurement uncertainty for

each analyte (MAUi, ppm) and known interferant (MIUk, ppm)

using appendix D of this addendum.       Verify that

(a) MAUi < (AUi)(DLi), FRUi < AUi, and FCUi < AUi for each

analyte and that (b) the CTS chosen meets the requirements

listed in sections 4.5.1 through 4.5.5 of this addendum.


5.0   SAMPLING AND ANALYSIS PROCEDURE

      5.1    Analysis System Assembly and Leak-Test.      Assemble

the analysis system.      Allow sufficient time for all system

components to reach the desired temperature.       Then,

determine the leak-rate (LR) and leak volume (VL), where VL =

LR tSS.     Leak volumes shall be ≤4 percent of VSS.

      5.2    Verify Instrumental Performance.   Measure the

noise level of the system in each analytical region using

the procedure of appendix G of this addendum.          If any noise

level is higher than that estimated for the system in
section 4.12 of this addendum, repeat the calculations of

appendix D of this addendum and verify that the requirements

of section 4.12 of this addendum are met; if they are not,

adjust or repair the instrument and repeat this section.

      5.3    Determine the Sample Absorption Pathlength.

Record a background spectrum.       Then, fill the absorption

cell with CTS at the pressure PR and record a set of CTS

spectra {R3}.      Store the background and unscaled CTS single

beam interferograms and spectra.       Using appendix H of this
addendum, calculate the sample absorption pathlength (LS)

for each analytical region.     The values LS shall not differ

from the approximated sample pathlength LS' (see section 4.4

of this addendum) by more than 5 percent.

    5.4   Record Sample Spectrum.    Connect the sample line

to the source.     Either evacuate the absorption cell to an

absolute pressure below 5 mmHg before extracting a sample

from the effluent stream into the absorption cell, or pump

at least ten cell volumes of sample through the cell before

obtaining a sample.     Record the sample pressure PS.
Generate the absorbance spectrum of the sample.     Store the

background and sample single beam interferograms, and

document the process by which the absorbance spectra are

generated from these data.     (If necessary, apply the

spectral transformations developed in section 5.6.2 of this

addendum).     The resulting sample spectrum is referred to

below as SS.

    Note:    Multiple sample spectra may be recorded

    according to the procedures of section 5.4 of this

    addendum before performing sections 5.5 and 5.6 of this

    addendum.

    5.5   Quantify Analyte Concentrations.    Calculate the

unscaled analyte concentrations RUAi and unscaled
interferant concentrations RUIK using the programs developed

in section 4 of this addendum.     To correct for pathlength

and pressure variations between the reference and sample

spectra, calculate the scaling factor, RLPS using equation
A.1,

                RLPS = (LRPRTS)/(LSPSTR)                (A.1)

Calculate the final analyte and interferant concentrations

RSAi and RSIk using equations A.2 and A.3,

                 RSAi = RLPSRUAi                          (A.2)

                 RSIk = RLPSRUIk                          (A.3)

       5.6   Determine Fractional Analysis Uncertainty.       Fill

the absorption cell with CTS at the pressure PS.       Record a

set of CTS spectra {R4}.     Store the background and CTS

single beam interferograms.        Using appendix H of this

addendum, calculate the fractional analysis uncertainty

(FAU) for each analytical region.        If the FAU indicated for

any analytical region is greater than the required accuracy

requirements determined in sections 4.1.1 through 4.1.4 of

this addendum, then comparisons to previously recorded

reference spectra are invalid in that analytical region, and

the analyst shall perform one or both of the procedures of

sections 5.6.1 through 5.6.2 of this addendum.

       5.6.1   Perform instrumental checks and adjust the

instrument to restore its performance to acceptable levels.

If adjustments are made, repeat sections 5.3, 5.4 (except

for the recording of a sample spectrum), and 5.5 of this

addendum to demonstrate that acceptable uncertainties are

obtained in all analytical regions.

       5.6.2   Apply appropriate mathematical transformations

(e.g., frequency shifting, zero-filling, apodization,

smoothing) to the spectra (or to the interferograms upon
which the spectra are based) generated during the

performance of the procedures of section 5.3 of this

addendum.    Document these transformations and their

reproducibility.    Do not apply multiplicative scaling of the

spectra, or any set of transformations that is

mathematically equivalent to multiplicative scaling.

Different transformations may be applied to different

analytical regions.    Frequency shifts shall be less than

one-half the minimum instrumental linewidth, and must be

applied to all spectral data points in an analytical region.

The mathematical transformations may be retained for the

analysis if they are also applied to the appropriate

analytical regions of all sample spectra recorded, and if

all original sample spectra are digitally stored.       Repeat

sections 5.3, 5.4 (except the recording of a sample

spectrum), and 5.5 of this addendum to demonstrate that

these transformations lead to acceptable calculated

concentration uncertainties in all analytical regions.
6.0   POST-ANALYSIS EVALUATIONS

      Estimate the overall accuracy of the analyses performed

in accordance with sections 5.1 through 5.6 of this addendum

using the procedures of sections 6.1 through 6.3 of this

addendum.

      6.1   Qualitatively Confirm the Assumed Matrix.    Examine

each analytical region of the sample spectrum for spectral

evidence of unexpected or unidentified interferants.       If

found, identify the interfering compounds (see Reference C
for guidance) and add them to the list of known

interferants.    Repeat the procedures of section 4 of this

addendum to include the interferants in the uncertainty

calculations and analysis procedures.    Verify that the MAU

and FCU values do not increase beyond acceptable levels for

the application requirements.    Re-calculate the analyte

concentrations (section 5.5 of this addendum) in the

affected analytical regions.

    6.2   Quantitatively Evaluate Fractional Model

Uncertainty (FMU).    Perform the procedures of either section

6.2.1 or 6.2.2 of this addendum:

    6.2.1   Using appendix I of this addendum, determine the

fractional model error (FMU) for each analyte.

    6.2.2   Provide statistically determined uncertainties

FMU for each analyte which are equivalent to two standard

deviations at the 95 percent confidence level.    Such

determinations, if employed, must be based on mathematical

examinations of the pertinent sample spectra (not the

reference spectra alone).    Include in the report of the

analysis (see section 7.0 of this addendum) a complete

description of the determination of the concentration

uncertainties.

    6.3   Estimate Overall Concentration Uncertainty (OCU).

Using appendix J of this addendum, determine the overall

concentration uncertainty (OCU) for each analyte.    If the

OCU is larger than the required accuracy for any analyte,

repeat sections 4 and 6 of this addendum.
7.0   REPORTING REQUIREMENTS

[Documentation pertaining to virtually all the procedures of

sections 4, 5, and 6 will be required.   Software copies of

reference spectra and sample spectra will be retained for

some minimum time following the actual testing.]

8.0 REFERENCES
A)   Standard Practices for General Techniques of Infrared

     Quantitative Analysis (American Society for Testing and

     Materials, Designation E 168-88).

B)   The Coblentz Society Specifications for Evaluation of

     Research Quality Analytical Infrared Reference Spectra
     (Class II); Anal. Chemistry 47, 945A (1975); Appl.

     Spectroscopy 444, pp. 211-215, 1990.

C)   Standard Practices for General Techniques for Qualitative

     Infrared Analysis, American Society for Testing and

     Materials, Designation E 1252-88.

D)   "EPA Traceability Protocol for Assay and Certification of

     Gaseous Calibration Standards," U.S. Environmental

     Protection Agency Publication No. EPA/600/R-93/224, December 1993.